The present invention relates to a safety system for a turbofan engine thrust reverser, more particularly such a safety system integrated into the hydraulic control system for the thrust reverser.
Turbofan engines are well known in the art and typically comprise a turbojet engine drivingly connected to a turbofan, usually mounted on the front of the turbojet engine. A turbofan housing, radially displaced from, but generally concentric with the turbojet engine housing defines a cold flow air duct for air driven by the turbofan. In such turbofan engines having a relatively high bypass ratio, thrust reversers are typically provided on the turbofan housing so as to redirect the air passing through the cold flow air duct during landing of the aircraft in order to provide a reverse thrust.
Thrust reversers may assume many different types, but a typical thrust reverser is illustrated in FIG. 1. The thrust reverser comprises a stationary, upstream portion 1 which forms a part of the turbofan housing, a movable portion 2 which redirects the air passing through the cold flow air duct and a stationary, downstream collar 3 which also forms a portion of the turbofan housing. The stationary, upstream portion 1 typically comprises an exterior panel 4 which defines a portion of the exterior surface of the turbofan housing, an internal panel 5 which, in conjunction with the housing for the turbojet engine (not shown) defines boundaries of the cold flow air duct and a frame 6 which interconnects panels 4 and 5. The frame 6 also supports the actuator 7a for controlling the movement of the movable portion 2, which in this instance comprises one or more movable thrust reversing doors 7. The number of such doors may vary depending upon the application of the turbofan engine to a particular type of aircraft and typically comprises 2, 3 or 4 such thrust reverser doors. These doors may be displaced around the circumference of the turbofan housing and, when in their deployed positions redirect the air passing through the cold flow air duct to provide the thrust reversing effect.
FIG. 2 illustrates a pair of such thrust reversing doors 7 in their deployed positions in which the forward, or upstream, edge is displaced radially outwardly from the generally annular turbofan housing. As is well known in the art, a rear, or downstream portion of the thrust reverser doors 7 extend inwardly into the cold flow duct so as to redirect the air outwardly through the turbofan housing and in a forward direction. Each such thrust reverser door 7 is operatively associated with a hydraulic jack or actuator 7a, which typically comprises a cylinder having an extendible and retractable piston rod attached to the thrust reverser door 7.
Such thrust reversers are well known in the art and typical examples of which may be found in U.S. Pat. Nos. 4,894,985; 4,858,430; 4,916,895; 4,914,905; 4,976,466; 4,960,243; and 5,039,171.
These types of thrust reverser doors have proven very effective in providing thrust reversing forces to the air frame with which the turbofan engine is associated and, quite obviously, serious problems may arise if the thrust reverser doors are deployed at an inappropriate time. Accidental initiation of the thrust reversal can cause catastrophic results to the aircraft. A number of devices are known designed to preclude such accidental deployment of the thrust reverser doors. In particular, a mechanical locking device on the thrust reverser door and the support structure are known, as well as a mechanical locking device on the thrust reverser control actuator. In some applications, however, such dual safety devices may be inadequate to preclude all risk of malfunctions, especially when the thrust reverser doors are strongly urged to move to their deployed, thrust reversal positions.
U.S. Pat. No. 4,297,844 illustrates a hydraulic control system for thrust reversers, while U.S. Pat. No. 4,437,783 describes an associated mechanical locking and detecting system for such thrust reversers. None of these known devices, however, have provided the requisite security for preventing the accidental deployment of a thrust reverser door.